EP 94850128.3 describes an active intake system for multiple cylinder combustion engines, comprising a first air distribution chamber, one separate inlet pipe for each engine cylinder, which inlet pipes extend between the first chamber and the respective inlet valve/valves of the cylinders. Also, there a second air distribution chamber which is connectable to each one of the inlet pipes between said first chamber and the inlet valves via a respective passage which passage can be opened by means of an operable throttle valve. The second chamber is connected to the first chamber via resonance pipes, the inlets to the second chamber being openable via a further throttle valve. This solution enables exploitation of the resonance frequency for an advantageous volumetric efficiency within the middle and upper engine speed ranges.
In many cases, it is desirable to instead provide a more advantageous volumetric efficiency within a lower range of engine speed. This is relatively simple to accomplish, but in that case it is normal to get a dip in the moment curve effecting the middle range of the engine speed. Such a dip is perceived by the driver of a vehicle, as if the engine lacks power in the middle range. Therefore, the normal driver tends to use unnecessary high revs in order to keep the engine out of the dip in the moment curve. This results in that the positive effect of the increased volumetric efficiency in reality disappears for these known arrangements.